Process for making devitrified products



United States Patent 3,117,881 PROCESE FOR MAKING DEVED PRGEEKJTS Kenneth M. Henry, Toledo, and William E. Smith, Sylvania, Ohio, assignors to (lwens-Illinois Glass Company, a corporation of (thin No Drawing. Filed Oct. 15, 1959, Ser. No. 845,551 34 Claims. ((ll. 106-39) The present invention relates to a process for making devitrified products of extremely high strengths and more particularly to a method of making a crystalline article by the controlled devitrification of a vitreous article.

The accidental or unintentional devitrification of glass has long constituted a problem in the glass-making art and, in the past, every effort has been expended to prevent the formation of crystals in glass, both during forming and annealing. It has now been found that by the deliberate conversion of a suitable, initially vitreous composition to a devitrified predominately crystalline structure, e.g., on the order of 90 to 95 crystalline, amazing physical properties, such as fiexural strength, can be obtained in the devitrified product. Flexural strengths on the order of 1000,000 to 150,000 pounds per square inch can be attained and flexural strengths in excess of 40,000 pounds per square inch are standard.

The deliberate conversion of a vitreous composition to a devitrified product, as accomplished by the method of the present invention, involves (l) the incorporation of a nucleating agent in the original vitreous composition and (2) the heat treatment of the vitreous composition through a heat treatment cycle to initiate and foster devitrification of the original composition to a substantially crystalline structure. The devitrification can be accom plished after formation of the vitreous composition to an article of the size and shape of the finished article, and no substantial distortion and only a small compensatable dimensional change occurs during the transition. Thus, conventional glass forming methods, such as pressing, blowing, tube and rod drawing, can be utilized to form the vitreous article prior to devitrification.

The present invention now proposes the utilization of a nucleating agent comprising a mixture of zirconia (ZrO and an additional oxide selected from the group consisting of TiO V 0 C00, NiO, MoO ,Fe O orThO The function of such a nucleating agent is to provide in the vitreous composition a myriad of submicroscopic crystallization centers, or nuclei, upon which grow the crystals subsequently formed by the vitreous composition during devitrification. Titania alone has earlier been suggested as a nucleant in similar devitrification processes. It has now been found that a mixture of zirconia and one of the aforementioned metal oxides can be more effectively utilized to yield high strength devitrified products from certain normally vitreous compositions when such compositions are melted, formed, and heat treated.

The heat treatment of the vitreous compositions of this invention occurs preferably in three phases; (1) a nucleation phase at substantially the annealing point (log viscosity 13.5), (2) a development phase slightly below the fiber softening point (preferably at a log viscosity ranging from log 8 to log 12), and (3) a crystallization phase at preferably 150 to 300 F. above the fiber softening point which is log viscosity 7.65. The development phase is of primary importance in developing a rigid crystalline framework throughout the article, thereby preventing deformation at the higher crystallizing temperature and insuring uniform later crystallization.

It is, therefore, an important object of this invention to provide an improved method for the devitrification of vitreous compositions to yield high strength, predominanuy crystalline products.

Another object is the utilization of a mixture of zircoma "ice and a second oxide as a nucleant in the devitrification of vitreous compositions.

It is a further object to provide a devitrification process wherein a vitreous composition containing relatively minor amounts (less than about 10%) of a mixture ZrO and a secondary nucleating oxide is devitrified according to a predetermined heat treatment to successively form submicroscopic nuclei throughout the vitreous composition and subsequently to form on said nuclei a crystalline structure in which 50 to 98%, and preferably from to of the original vitreous composition is crystalline.

Yet another object is the devitrification of an article of vitreous composition containing a mixture of zirconia and a secondary nucleant oxide by subjecting the vitreous composition to a temperature corresponding to a viscosity ranging from log 8 to log 12 to develop a rigid crystalline framework in the article.

Other and further objects of this invention will become apparent from the following description:

BASE COMPOSITEONS Broad Range Preferred Range SiOz 40 to 70% AlsOa 15 to 35% h1g0 5 to 15% 40 to 60%. 17 to 32%. 6 to 12%.

Such preferred base compositions are selected so that the primary crystalline phases upon devitrification will lie within the various fields of mullite, cordierite, sapphirine, tridyrnite, etc., of the phase diagrams of the systems Al o fiSiO and MgOAl O SiO By selection of the MgOAl O SiO ratio, the devitrification products may be varied and the predominant crystalline phases of the final product can be preselected.

In general, it can be shown from examples contained herein that the maximum strength that can be developed in a given composition is dependent to a certain extent on the predominant crystalline phase present. It has been found that increasing strength is developed in the order cordierite-mullite-tridymite in moving from one predominant phase to the next.

Table I shows examples illustrating the preferred limits as described above.

Examples illustrating preferred SiO A1 0 and MgO composition limits:

Table l Ingredient Percent by Weight HEAT TREATMENT F.)

Hours at 1 600-1 1 750-1 [1, sac-1y 11 sou-1% MODIFYING AGENTS Various modifying agents can be added to the base compositions, which consist esentially of SiO A1 and MgO as hereinbefore set forth, to vary the melting and forming characteristics of the vitreous composition and to vary the degree and readiness of devitrification.

In general, oxides or fluorides of alkali metals or alkaline earth metals can be added to improve the melting characteristics of the batch. Such fiuxing agents are added to the batch at the expense of all other components or at the expense of other alkaline earth oxides (primarily MgO). Generally, excessive amounts of such fluxing agents reduce the final strength of the crystalline product and therefore the hereinafter recited preferred limits are to be desired.

Tin oxide (311%). While not considered a fluxing agent when present in small quantities as described here, is useful as an oxidizing agent and assists in fining and homogenizing the glass.

Exemplary of alkali metal salt fluxing agents are sodium fluoride, sodium oxide, potassium fluoride, potassium oxide, lithium fluoride, and lithium oxide.

A particularly useful modifying agent is calcium fluoride, which not only benefits melting and forming of the glass, but also promotes devitrification by developing a non-deforming skeletal framework of crystallites at temperatures below the deformation range of the glass. To prevent excessive fluorine losses during melting, 2% or less CaF is preferably utilized.

Both lithium oxide and lithium fluoride are excellent promoters of melting and when present in limited quantities are also promoters of devitrification. (See Tables IV and V.)

Boric oxide, a fluxing agent, is also extremely useful in controlling the relative amounts of glassy matrix and crystalline material. B 0 also lowers the thermal expansion coeflicient of the finished product. (See Table VI and VII.)

Another method for controlling the crystal-glass ratios in the finished product is the addition of small quantities of non-devitrifying glass composition which can be added as the oxides or more conveniently as cullet. Examples in Table XIII contain 5 and respectively of a typical soda-lime glass added as cullet.

To summarize the various modifying agents, the following modifiers may be used in the following amount expressed as parts by weight of the total batch:

This list should not be construed as containing all the possible modifying agents but is merely indicative of the relative quantities of modifiers that can be added to the NUCLEATING AGENTS The utilization of a mixture of Zr0 and a secondary nucleant oxide has been found to yield consistently high strength materials, particularly where compositions are used which are at or near the actual composition point of cordierite (2MgO-2Al O -5SiO located in the primary phase field of mullite (3A1 O -2SiO in the phase diagram. Secondary crystalline phases in the final product may include sapphirine (4MgO-5Al O -2SiO tridymite (SiO spinel (Al O -Mgo), and zirconia (ZI'OZ).

The preferred nucleating agents of this invention fall within the range of at least 6.0% ZrO and from 1.0 to 1.75% of a secondary nueleant selected from the group consisting of TiO CoO, NiO, V 0 M00 Th0;, and Fe O No advantage is obtained from utilizing more than about 8% ZrO in combination with such a secondary oxide and the single combination of 7% ZrO and 1.5% TiO forms a preferred nucleant mixture of this invention. (See Table VI, Example 12.)

MELTING AND FORMING The batch, consisting of the base MgO-Al O -SiO composition, any modifying agents, and the nucleating agent, is melted by any normal glass melting procedure and apparatus. Due to the composition, a somewhat hig er than normal melting temperature of between about 2600 F. to 3000 F. is utilized.

Forming of the initial vitreous article can be carried out by any of the well-known glass forming operations of drawing, blowing, pressing or the like. Suitable forming temperatures for such compositions average somewhat higher than normal, as would be expected. The forming temperature of such compositions averages about F. below the melting temperature and ranges from about 2500" F. to about 2800 F.

HEAT TREATMENT Apparently, though not so far proved conclusively, the crystallization takes place during heat treatment through successive stages.

More specifically, these stages, in the preferred embodi ment of this invention, are as follows:

A. The maintenance of the composition, actually as the formed vitreous article, at a temperature corresponding substantially to the annealing point (viscosity of log 13.5). The material is held, thus, at substantially the annealing temperature with a variation of from about 20 F. below the annealing temperature to about 50 F. above the annealing temperature. The holding of the composition at this temperature leads to the formation of submicroscopic crystals of the nucleating agent dispersed throughout the glassy matrix. This heat treatment stage is hereinafter termed the nucleation stage.

B. The maintenance of the article, after nucleation, at a temperature corresponding to a viscosity of log 8 to log 12, preferably at log 8. For any given original composition, this temperature is preferably about 10 to 30 F. below the fiber softening point. During this heat treatment stage, the base composition will partially crystallize and a rigid, porous crystalline structure is predominantly formed from the base composition ingredients and not from the nucleating agents. The sub-microscopic nuclei dispersed in the glassy matrix at the end of the nucleation stage serve as the growth centers for the rigid framework formed during this second or development stage of the heat treatment cycle.

This development stage is necessary in most, though not all, compositions described herein. Its purpose is to provide a rigid skeletal crystalline framework to support the remaining glassy matrix when the temperature is raised above the fiber softening point to complete crystallization. The importance of such a development treatment, as indicated by strength determinations, is well pointed out in Table XII.

C. Finally, the rigidified framework and predomiantly glassy matrix from the development portion of the heat treat cycle is crystallized to substantial completeness by the maintenance of the article at a temperature 150 to 300 F. above the fiber softening point (log 7.65) of the original glass composition. The term substantial completeness is used to indicate complete so far as desired. For maximum physical properties, a completeness of 90 to 95% crystalline is usually desired, although the degree of completeness can be varied over a much wider range, 50-98%, by varying the heat treatment to obtain other or different physical properties.

This last stage actually results in the conversion of the majority of the composition to a crystalline structure and thus is known as the crystallization stage.

In each of the following examples except those in Table XH, the heat treatment has been carried out in three successive stages at the specified temperatures for the specified times. In actual practice, it has been found that the maintenance of a strict time and temperature schedule as above set forth may not be necessary. For example, it is sometimes feasible to maintain the nucleation temperature as described and then pass directly to the crystallization stage by merely passing through the development stage. However, very few of these compositions can be heat treated in this fashion without some deformation and loss of strength. In cases where these factors are not too important, considerable time can be saved. In any event, the entire heat treat cycle can be carried out in a single lehr with the lehr belt continuously advancing the article through successive nucleation, development, and crystallization zones.

FLEXURAL STRENGTH DETERMINATIONS To determine the flexural strengths of samples as hereinafter set forth, the following technique was utilized:

Preparation of Samples Lengths of cane were drawn from a crucible of the described molten glass. Sample cane diameters averaged about 0.100. After cooling, the lengths were cut into 2 /2" sections and divitrified according to the appropriate heat schedule. After devitrifications, the diameter of each sample was measured with a micrometer. Prior to testing, each sample was abused or abraded with 320 mesh grit paper.

When large tank melts were made, 0.4" and 0.5" diam eter rods were vacuum drawn from the melt. These rods were given the same treatment as above.

Testing.-All samples were tested on an Instron machine as simple beams using 3 point, center loading. The sample cane lengths were tested over a 2" span while the larger rod lengths were tested over a 4" span. All samples were tested at a rate of loading of 0.1" per min. which means that the load is applied through constant movement of the crosshead. The Instron was capable of accurate testing at loads ranging from 2 grams to 10,000 lbsiless than 1%. The load is automatically recorded on an X--Y recorder.

Calculati0n.--Calculation of flexural strength from breaking load and sample diameter was made using the standard formula for flexural stress at the extreme fiber:

Moment f Section modulus Since most samples were elliptical rather than circular in cross-section, the section modulus was calculated using the ellipse formula. The moment for a simple beam with a concentrated center load was calculated from the standard formula.

The number of samples tested varied; at least four samples were tested for each composition and the value given in each example is an average value.

The following glass composition was prepared and melted:

Table III BASE COMPOSITION Ingredient (Example 1): Percent by weight sio 47.2 A1 0 31.0 Mgo 11.25 NaF 0.73 ZrO 8.0 T10 1.5 SD02 Test samples were drawn from the melted composition and heat treated according to the schedule:

1.5 hours at 1420 F. 1.5 hours at 1740 F. 1.5 hours at 1950 F.

The heat treated samples were tested for flexural strength as above described and flexural strengths averaging 60,000 pounds per square inch were determined.

'It was determined by X-ray analysis that the heat treated samples were well devitn'tied within the range of from to crystalline and that the predominate crystalline phase 'was mullite with sapphirine and tridyrnite as secondary phases.

To determine the effect of Li O additions on the base composition, the following compositions were prepared and melted:

Table IV EFFECT OF L10 Percent by weight Examples -1 1 2 3 4 5 6 Ingredient REATMENTS F.)

Thus it will be seen that Li O in limited quantity acts as a devitrification promoter and dramatically increases the flexural strength of the devitrified product; however, the effect is lost as the amount increases beyond 1.0%. It should be emphasized that even the lowest values shown here still represent usable materials.

To assess the effect of LiF additions to the base como 7 position, the following compositions were prepared and The eifect of B 0 was studied by the replacement of melted: a portion of the A1 0 content of the base composihon Table V I 5 as follows:

EFFECT OF LiF TABLE VII Percent by Weight EFFECT OF 3.0 Examples 1 7 8 9 10 11 Ingredient: 10 P b W 11 S104. 47.2 47.5 47.2 47.2 47.2 47.2 cent 61g t A1203" 31. 0 31. 2 31. 0 31.1 31.1 31,1 MgO 11. 11. 1 ll. 0 10. 5 10. O 9. 5 Examples 3 15 1 7 1 NaF 1.0 ZrOz 8. 0 8. 0 8. 0 8. 0 8. 0 s. 0 T101 1. 5 1. 5 1. 5 1. 5 1. 5 1. 5 Ingredient; 15 010 40.0 40.0 40.0 40.0 40.0 L11? 0.5 1.0 1.5 2.0 3.0 3&3 2110 27 5 2&5 5 11.2 11.2 11.2 11.2 11.2 HEAT TREATMENT F.) 1.5 1.5 1.5 1.5 1.5 1, 450 1,450 1,450 1,450 1,450 1,450 02 0'2 (12 0,2 M 1.5 hOLiIS at 1, 740 1, 720 1, 720 1, 720 1, 720 1, 770 Q 75 0 75 75 0 75 0 75 Flexural Strengths HEAT TREATMENT F.)

(p.s.i.) 00,000 140,770 131,500 108,310 00,010 40,770

1,400 1,450 1, 450 1, 450 1, 450 CRYSTALLINE PHASESPRED0MINANT 0 1,5 hours at: 1, 700 1,080 1,700 1,050 1,680 [Examples] 1,950 1,980 1,050 1,020 1,080

Flexural Strength .s.1.)-- 101,520 57,140 42,800 51,840 00,400

Mullite Tridy- Tridy- Trldy- Cordier- Mullite. 3O

mite. mite. mite. ite. Tridy- Sapphir- Sapphir- Sapphlr- 1\[llllit6 Tridy- Examples" 3 15 i 16 17 18 mite. ine. ine. ne. mite .3 3 Mumw- 02 Mullite 01011100.- Mullite 1011111110-. Sapphirine. 1 Crystalline Sapphir- Sapphir- Sapphir- Sapphir Enstatite.

Phases. Tinle. ine. ine. ine. From examples above it will be seen that MP in 3 amounts ranging from 0.5 to 2.0% of the composition dramatically mcreases the fiexural strength when sub- Examples w 3 15 16 17 18 stituted for NaF and MgO in the base composition. In amounts greater than about 2.0% LiF, no material bene- Coeifieient of Expansion (0 fit is realized. It should be noted that the lithium ion to 300 F 10-7) 110.0 100.0 87.3 52 48 and the fluorine ion are the important additives and may be added separately as MgF or AlF and hi CO or spodurnene.

Once the glass is melted, the manner of addition of Thus the substitution of B 0 for a part of the A1 0 either ion i i aterial, although losses of fluopine will content generally decreases the fiexural strength but lowbe less if highly stable fluoride salts are used. (See Table ers the coeflicient of expansion as the B 0 content is in- VI.) 7 creased from 2.0% to 5.0%.

Table VI B 0 can also be substituted for a portion of the SiO 2 EFFECT OF OTHER FLUORIDES ADDED AS L120 03) A1 0 combined content 01 the base compositions, as fol- 00 lows:

Percent by Weight Examples 12 (F2 13 (F; 14 (F2 added as added as added as Table VI LiF) MgFz AlFs Ingredient: Percent by Weight A1F1 1.08 Examples 19 20 21 22 23 MgO 10. 7 11.1'

L50. 0. 58 0,58 60 Ingre ient:

LiF 10 46.6 40.3 45.7 45.1 43.9

ZrOz 7.0 7 0 30.3 30.1 20.7 20.3 28.5

- 1,080 1,680 1,080 1.5 hours at; 1,950 1,950 1, 980 HEAT TREATMENT R) Flexnral Strength (p.s.1.) 100,730 133, 540 110,100 1,450 1, 450 1,450 1, 450 1,450 1.5 hours at 1, 700 1, 700 1, 700 1, 700 1,080 1,050 1,050 1,950 1,050 1,000

Tridymite. Tridymlte. Tridymite. Crystalline Phases Mullite Mullite.-- Mullite.

V Sapphirine Sappnirine Sapphirine. 7 Flexnral Strength (p.s.i.) 76,620 84,440 54,460 62,000 41,070

Table VII1-Continued Table XI Examples 19 20 21 22 23 Percent by Weight Mullite. Mu11lte Mnllite Mulliteu Sapphirlne. Examples 31 32 33 34 35 36 37 Crystalline Sapphir- Sapphir- Sapphir- Sapphir- Phasesnn ine. ine. ine. ine.

Tridy- Tridy- Ingredient:

mite. mite. s: 47.6 47.6 47.6 47.6 47.0 47.6 47.6 .3 .3 31.3 .3 31.3 31.3 91.3 .1 .1 .1 .1 11.1 11.1 11.1 .0 .0 .0 .0 1.0 1.0 1.0 E amp s 19 0 2 22 23 1O .0 O 80 .2 .2 .2 .2 0.2 0.2 0.2

Coefiicient oi Expansion (0 to 300 F. 10- 104.1 106.2 58.3 57.2

Although the substitution of B 0 for the combined SiO --Al O content lowers the coefiicient of expansion, the flexural strength is also lowered, becoming less than 45,000 p.s.i. when the S10 content drops below 45%.

The minimum amount of ZrO necessary as a nucleant was tudies as follows: 1110117. at: {1,450 1,400 1,450 1, 450 1,450 1,450 1,425 1,680 1, 550 1, 680 1,680 1, 680 1, 950 1,690 Table IX 151115.111 1,950 1,900 1,950 1,950 1,950 1,950 1,780

EFFECT OF Z104 CONTENT Flexural Strength Percent by Vveight (p.s.i.) 160,730 32,340 73,100104,100 54,410 80,230 42,570

Examples 2 24 25 26 27 28 Crystalline Phases Tndymite -Pre dominant. Mullite Ingredient: Sapphmne i2 2 @912 if}, 11 2 i 32 To determine the effect of the heat treatment cycle g 6 -g upon the final developed strength of the devitrified comj 5 5 5 positions, the composition of Example 3 of Table IV was 1 5 5 1. 5 5 5 5 melted and heat treated as follows: 0.2 0.2 0.2 0.2 0.2 0.2

Table XII HEAT TREATMENT a R) EFFECT OF DEVELOPMENT TEMPERATURE ON STRENGTH h {1,42 1,45 1,420 1,420 1,420 1,42 1.5 ours at 1,72 1, 1,720 1,720 1,720 1,7 0

1,950 1,950 1,950 1,950 1,950 1,950 Heat Treat Temperature Stren th Flexural Strength 40 (p.s.i,) 114,250 107,190 75, 520 78,130 82, 890 40,970 Nucleatm 5,253,? Mullite gfgggf gg Sapphirine 1,420 None 1,950 19,780 Tnd mrte 1, 420 1, 700 1, 950 78, 940 1, 450 None 1, 980 56, 660 1, 450 1, 650 1, 980 77, 770 Thus it will be seen that nucleating etfimency as shown 1,509 None 1,930 114,350 1, 500 1, 680 1, 980 123, 870 by strength of the materlal falls 0E considerably when the Z10 content drops below 6.0% or the combined ZrO TiO drops below 7.5%

Table X COLIPARISON OF ZrOz-T 102 WITH T102 ALONE HEAT TREATMENT F.)

l, MO-1% Hours at 1, 6804M) 1, 950-1% Flexural Strength (p.s.i.) 160, 730 79, 210

Tridymite Crystalline Phases Mullite Sapphirine Examples illustrating secondary nucleating agents in combination with ZrO In each instance, the maintenance of the article at a development temperature resulted in the development of 5 greater strength in the final product.

Examples of compositions modified by addition of sodaline cullet:

Table XIII Percent by Weight Example 38 39 Heat Treatment F.

1, 420 1, 420 1.5 hours at 1, 650 1, 650 1, 920 1, 950

Flexurai Strength (p.s.i.) 120, 420 60, 740

. Mullite Mullite. Crystanme Phases {Sapphirine Sapphirine.

it Thus, soda-lime glass cullet can be added to the base composition, so as to vary its composition and the crystalto-glassy matrix ratio in the final devitrified product.

The embodiments of the invention in which an exclusive property or privilege is claimed, are defined as follows:

1. In a method of making a devitrified product, the steps of melting glass batch materials and forming a glass consisting essentially of:

Ingredient- Percent by weight SiO 40 to 60 A1203 t MgO 6 to 12 ZrO At least 6 and a secondary nucleant, said secondary nucleant being present in an amount less than 2 weight percent, the sum of ZrO' and said secondary nucleant being at least 7.5 weight percent of the glass, and heat treating the resulting glass until a crystalline product containing at least 50 weight percent crystalline material is obtained.

2. The method of claim 1, wherein the secondary nucleant is selected from the group consisting of TiO M003, Fezog, V305, COO, and T1102.

3. A method as defined in claim 2, wherein the batch also contains:

4. A method as defined in claim 2, wherein the batch also contains a material selected from the following group in the indicated amounts:

Ingredient- Percent by weight 9131(1); 0:05-1 a 0.05-1 Na O 0.05-1 K 0 0.05-1 CaF 0.05-2 lilii? 0.05-2 0.05-2 B 0 0.05-3 CaO 0105-5 PbO 0.05-2 BaO 005-2 5. A method as defined in claim 2, wherein the Z content of the glass is about 7% by weight and the secondary nucleating oxide content is about 1.5% by weight of the batch.

6. A method as defined in claim 2, wherein the heat treatment comprises successively maintaining, the composition at temperatures corresponding to viscosities of log 13.5, log 8 to log 12, and a range of from 100 F. to 300 F. above log 7.65.

7. A method as defined in claim 2, wherein the secondary nucleating oxide is TiO 8. In a method of making a devitrified product, the

I steps of melting and forming a glass consisting essentially of:

Ingredient- Percent by weight SiO 40 to 70 A1 0 to 35 MgO 5 to 15 ZrO At least 6 and a secondary nucleant, formingan article from said glass, forming subrnicroscopic nuclei in the article, maintaining the article at a development temperature corresponding to a viscosity of log 8 to log 12 for a period of time sufiicient to develop a rigid crystalline framework in the article, and subsequently substantially completely crystallizing the remainder of the article, said secondary nucleant being selected from the group consisting of TiO M00 FeO V 0 C00, NiO and ThO the sum of ZrO and said secondary nucleant being at least 7.5 weight percent of said glass.

9. The method of claim 8, wherein the nuclei are formed at a temperature corresponding substantially to the annealing point and the crystallization occurs at a temperature corresponding to F. to 300 F. above log 7.65

10. In a method of making a devitrified product, the steps of melting and forming a vitreous composition consisting essentially of Percent SiO 40-70 A1 0 15-35 t t-P 0 1 ZrO At least 6 and a secondary nucleant, and heat treating the formed vitreous composition to devitrify the same, said secondary nucleant being selected from the group consisting of Tloz, B11003, F6203, V205, COO, and T1102, and the sum of Zr0 and said secondary nucleant being at least 7.5 weight percent of the product.

11. In a method of making a devitrified product, the steps of melting and forming a vitreous composition consisting essentially of Percent SiO 40-70 A1 0 15-35 1 1 5 5?? 1 2 ZrO At least 6 Percent SiO 40-70 A1 0 15-35 5)" 5?? 2 3 I ZrO At least 6 and a secondary nucleant and heat treating the formed vitreous composition to devitrify the same, said secondary nucleant being selected from the group consisting of TiO M00 Fe O V 0 C00, NiO, and T and the sum of ZrO and said secondary nucleant being at least 7 .5 weight percent of the product.

'13. In a method of making a devitrified product, the steps of melting and forming a vitreous composition consisting essentially of 7 Percent Si0 40-70 A1 0 15-35 lSVIgOO 5-15 11 2 0-5-2 ZrO At least 6 and a secondary nucleant, and heat treating the formed vitreous composition to devitrify the same, said secondary nucleant being selected from the group consisting of TiO;,;, M00 Fe O V 0 C00, NiO, and ThO and the 13 sum of Zr and said secondary nucleant being at least 7.5 weight percent of the product.

14. In a method of making a devitrified product, the steps of melting and forming a vitreous composition consisting essentially of Percent SiO 40-70 A1 0 15-35 MgO 5-15 NaF 0.5-3 ZrO At least 6 Ingredient Percent by weight sio -5 40 to 70 A1203 to MgO 5 to 15 ZrO At least 6 and a secondary nucleant selected from the group consisting of TiO M00 'Fe O V 0 C00, and NiO, and T110 in an amount less than 2 weight percent, the sum of the ZrO and said secondary nucleant being at least 7.5 percent of the composition, to effect the formation of a myriad of submicroscopic nuclei distributed throughout the vitreous mass, the improvement of developing a rigid crystalline framework by heating said nucleated mass to a temperature corresponding to from about 10 to 30 F. below the fiber softening point of said composition and maintaining said temperature for a period of time sufficient to develop in said mass a rigid skeletal crystalline framework.

16. In a method of making a devitrified product from a melted and formed vitreous mass consisting essentially of:

Ingredient- Percent by weight SiO 40 to 70 A1203 to MgO 5 to ZrO At least 6 and a secondary nucleant selected from the group consisting of TiO M00 Fe O V 0 C00, and NiO, and ThO in an amount less than 2 weight percent, the sum of the ZrO and said secondary nucleant being at least 7.5 percent of the mass, the steps of heat-treating the mass in accordance with the following schedule:

A. Maintaining the mass at a temperature from F. below to 50 F. above the annealing temperature to develop submicroscopic nuclei therein;

B. Maintaining the nucleated mass at a temperature of from 10 F. to F. below the fiber softening point to develop a rigid crystalline framework therein; and

C. Maintaining the article at a temperature of from 150 F. to 300 F. above the fiber softening point to substantially completely crystallize the mass.

17. A thermally crystallizable glass having the following composition:

and a secondary nucleant in an amount less than 2 weight percent, the sum of ZrO and said secondary nucleant being at least 7.5 weight percent of the composition.

14 18. The glass of claim 17 wherein the secondary nucleant is selected from the group consisting of TiO M00 Fe203, V205, COO, and T1102,

19. The glass of claim 18 wherein the composition also contains:

Ingredient Percent by weight S1102 NaF 03 N320 0-2 K 0 0-3 CaF 0-8 Li O 0-5 LiF 0-5 B 0 05 CaO 0-10 PbO 0-5 BaO 0-l0 20. The glass of claim 18 wherein the composition also contains a material selected from the following group in the indicated amounts:

Ingredient- Percent by weight Sn0 0.05-1 NaF 0.05-1 Na O 0.05-1 K 0 0.05-1 CaF 0.05-2 Li O 0.052 LiF 0.05-2 B 0 0.05-3 CaO 0.05-5 PbO 0.05-2 BaO 0105-2 21. The glass of claim 17 wherein the ZrO content is about 7% by weight and the secondary nucleant content is about 1.5% by weight.

22. The glass of claim 17 wherein the secondary nucleant is TiO 23. A method of claim 1 wherein said heat treatment is efiected to obtain a product that is -95 weight percent crystalline.

24. A thermally crystallizable glass having the followmg composition:

Ingredient Percent by weight SiO 40 to 70 A1203 t0 MgO 5 to 15 ZrO At least 6 and a secondary nucleant selected from the group consisting of TiO M00 Fe O' V 0 C00, NiO, and Th0; in an amount less than 2 weight percent, the sum of the ZrO and said secondary nucleant being at least 7.5 percent of the composition.

25. A devitrified product consisting essentially of 40 to 70 weight percent SiO 15 to 35 weight percent A1 0 5 to 15 weight percent MgO, and at least 6 weight percent ZrO and a secondary nucleant, said product being crystallized to substantial completeness, and said secondary nucleant being selected from the group consisting of Tioz, M003, F6203, V205, COO, and T1102, and the sum of ZrO and said secondary nucleant being at least 7.5 weight percent of the product.

26. A product of thermal devitn'iication of a glass consisting essentially of 40 to 70 weight percent SiO 15 to 35 weight percent A1 0 5 to 15 weight percent MgO, at least 6 weight percent ZrO and a secondary nucleant, said product consisting of 50-98 Weight percent crystals dispersed in the 502 weight percent vitreous material, and said secondary nucleant being selected from the group consisting of TiO M00 Fe O V 0 C00, NiO and ThO the sum of ZrO and said secondary nucleant being at least 7.5 weight percent of the product.

27. A product of claim 26 wherein said secondary nucleant comprises V 0 28. A product of claim 26 wherein said secondary nucleant comprises Fe O 28. A product of claim 26 wherein said secondary nucleant comprises NiO.

30. A product of claim 26 wherein said secondary nucleant is 1-1.75 weight percent TiO 31. A product of claim 26 which also contains 0.05-2 weight percent CaF 32. A thermally crystallizable glass having 40-70 weight percent SiO 15-35 weight percent A1 5-15 weight percent MgO, at least 6 weight percent ZrO and an oxide selected from the group consisting of TiO;, M00 Fe O V 0 COO, NiO, and ThO in an amount less than 2 weight percent, the sum of the ZrO and the selected oxide being at least 7.5 but less than 10 weight percent of the composition.

33. A product of thermal devitrification of the glass consisting essentially of 40-70 Weight percent SiO -35 weight percent A1203, 5-15 Weight percent MgO, at least 6 weight percent ZrO and an oxide selected from the group consisting of the group TiO M00 Fe O V 0 C00, NiO, and ThO the sum of said ZrO and said selected oxide being at least 7.5 but less than 10 Weight percent of the glass, the product consisting essentially of at least 50% crystalline material dispersed in the vitreous material left after the thermal devitrification of said glass.

34. In a method of making a product of crystallization of glass, the steps of melting glass batch ingredients to produce a glass consisting essentially of 40-60 weight percent S10 17-32 weight percent A1 0 6-12 weight percent MgO, at least 6 weight percent of ZrO and an oxide selected from the group consisting of TiO M00 Fe O V 0 C00, NiO, and ThO said Zr0 and said selected oxide being at least 7.5 but less than 10 weight percent of said glass, and heat treating the resulting glass composition until a crystalline product containing at least crystalline material is obtained.

References Cited in the file of this patent UNITED STATES PATENTS 1,086,113 Wolf-Burckhardt et al. Feb. 3, 1914 1,394,296 Fisher Oct. 18, 1921 2,779,136 Hood et al. Jan. 29, 1957 2,873,197 McMullen Feb. 10, 1959 2,920,971 Stookey Jan. 12, 1960 3,006,775 Chen Oct. 31, 1961 3,022,179 Morrissey Feb. 20, 1962 3,022,180 Morrissey et al. Feb. 20, 1962 FOREIGN PATENTS 1,082,016 Germany May 19, 1960 1,099,135 Germany Feb. 9, 1961 OTHER REFERENCES Chemical Abstracts, July 10, 1959, item 12615c, Vitrokeram.

Harmon: Ceramic Industry, New Concept Is Basis for Developing New, Better Ceramics, August 1959 (pages 52-53).

UNITED STATES PATENT OFFICE CERTIFICATE 0F CQREC'HON Patent No, 3, ll7 88l January 14 1964 Kenneth M Henry et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 23 for "1000,000 read 100,000 column 5 line 52, for "devitrifieations" read devitrification column 9 line 20, for "studies" read studied column 10, lines 51 and 52 for "soda line" read soda lime column 12 line 8 for "FeO read Fe O Q Signed and sealed this 16th day of June 1964.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Aitesting ()fficer Commissioner of Patents 

1. IN A METHOD OF MAKING A DEVITRIFIED PRODUCT, THE STEPS OF MELTING GLASS BATCH MATERIALS AND FORMING A GLASS CONSISTING ESSENTIALLY OF: 